Avoiding Graft-Tunnel Length Mismatch in Anterior Cruciate Ligament Reconstruction: The Single–Bone Plug Technique

Abstract

Anterior cruciate ligament reconstruction, using autogenous bone–patellar tendon–bone (BTB) as a graft material, is commonly performed in the setting of anterior cruciate ligament insufficiency. Although bone–patellar tendon–bone autograft has an extensive track record, showing excellent clinical results, donor-site morbidity and graft-tunnel mismatch can still be problematic for a subset of patients. In the setting of a tendon graft that is too long, adequate interference screw fixation cannot be obtained, typically resulting in a tibial-sided bone plug that achieves less than 15 to 20 mm of bone in the distal tibial tunnel. We present an easy and effective technique for avoiding the graft-tunnel mismatch problems that commonly occur in patients who have an excessively long patellar tendons. This technique involves a simple preoperative planning algorithm that ultimately results in a single tibial-sided plug harvest. Bony interference fixation is then obtained on the femoral side and soft-tissue fixation on the tibial side. This technique allows for satisfactory graft fixation while avoiding the donor-site morbidity associated with patellar bone plug harvest.

Rupture of the anterior cruciate ligament (ACL) remains one of the most common intra-articular injuries to the knee joint, with an estimated annual incidence ranging between 100,000 and 200,000.¹ Reconstruction of the torn ligament continues to be the treatment of choice for young active patients who frequently participate in activities that require pivoting and cutting. Numerous tendon autogenous and allograft options exist for ligament substitution, with patellar tendon and hamstring tendon being the most common autograft alternatives used. Each graft type is associated with its own inherent set of risks and benefits. From a clinical perspective, patellar tendon graft is widely used and enjoys an extensive, successful track record. The intrinsic advantage of osseous aperture fixation, offered by the graft, is often cited as one of the underlying reasons for the success of bone–patellar tendon–bone (BTB) autograft.² However, the risks of graft-tunnel length mismatch and donor-site morbidity resulting from bone plug harvest should not be considered negligible.

We suggest an easy and reliable method for avoiding the pitfalls associated with an excessively long patellar tendon, with the use of a single bone plug harvested at the tibia (Table 1). This technique allows for dependable osseous aperture fixation on the femoral side combined with soft-tissue fixation on the tibial side. Graft obliquity is maintained, and the donor-site morbidities related to patellar bone plug harvest are avoided. Patients who may benefit from this technique are identified through preoperative measurement of the overall length of the tendon by magnetic resonance imaging (MRI) that is then confirmed at the time of the operation.

Table 1.

Key Points for Appropriate Use of Single–Bone Plug Technique During ACL Reconstruction, Including Indications, Pearls, and Pitfalls for Successful Implementation of Technique

Indications

Patients indicated for ACL reconstruction using BTB autograft, in whom graft-tunnel length mismatch may occur

Patients who possess a minimum patellar tendon length of 60 mm

Pearls

Proper perioperative planning must take place to allow for surgical success, including preoperative patellar tendon length measurement on sagittal MRI sequences with confirmation of tendon length in the operative suite after tibial plug harvest.

Harvest of the periosteum overlying the patella can aid in control of the graft during intra-articular passage and tibial fixation.

Without harvest of a patellar bone plug, patients can expect less quadriceps inhibition and less overall swelling in the perioperative period.

A single-plug harvest will allow the surgeon to maintain appropriate tunnel obliquity and position on the anterior tibial cortex in the face of an excessively long patellar tendon.

Pitfalls

Improper perioperative planning that results in an excessively short graft (typically occurring in patients who have a patellar tendon length <60 mm)

Technique

Preoperative Planning

Patients are first identified as surgical candidates in the outpatient setting after a thorough history and physical examination. Preoperative MRI is used to confirm the clinical suspicion of ACL insufficiency and rule out other concomitant knee pathology. Furthermore, a dedicated knee MRI study is essential to identify patients who will benefit from this technique according to the overall length of their patellar tendon. Specifically, T1 sagittal images are reviewed to identify the image on which the tendon shows its shortest midsubstance distance, as measured from its origin on the inferior portion of the patella to its insertion on the tibial tubercle. Accordingly, the tendon's length is measured and recorded by use of standard MRI computerized measurement tools. If this length is greater than or equal to 60 mm (Fig 1), the single-plug technique can be used. When at least 60 mm of tendon length is combined with a 20-mm bone plug from the tibial side, an overall graft length of 80 mm will be created. Eighty millimeters allows for adequate substitution of the ACL because the intra-articular length of the ligament has been shown to average between 25 and 30 mm.^3,4

Fig 1.

Sagittal T1 image showing patellar tendon length measurement.

Surgical Technique

Once the appropriate patient has been indicated for this single–tibial plug technique, standard preparation, draping, and patient positioning can be used. We elect to use a longitudinal incision that begins just proximal to the inferior pole of the patella and extends just distal to the tibial tubercle. The incision is centered medial to the midline so that the patient will not have to directly kneel on his or her healed incision, and thus the path of the tibial tunnel may be incorporated into the skin harvest incision. Elasticity of the skin overlying the patella typically allows for minimal dissection proximally with maintenance of excellent exposure. Central-third tendon harvest is then accomplished with the use of a No. 10 surgical blade, and the tibial bone plug is extracted in a rectangular fashion with the aid of an oscillating saw. Bone block width is dictated by the tendon harvest and may range from 9 to 11 mm, whereas bone block length should range from 20 to 25 mm to allow for adequate bone-bone healing of the graft. Once the tibial bone plug has been safely harvested, it is controlled with a moist lap pad and attention is then turned toward the proximal portion of the graft.

The origin or takeoff of the patellar tendon graft from the inferior pole of the patella is directly visualized by translating the graft in a cephalad fashion to view its undersurface. At this point, overall tendon length is confirmed with the aid of a ruler, intraoperatively, to ensure that the length correlates with the preoperative MRI measurements (Fig 2A). Double-checking the tendon length ensures proper total length of the graft before commitment to the single-plug harvest. Careful dissection is then undertaken with a No. 15 surgical blade to remove the tendon from the inferior pole of the patella in continuity with a full-thickness strip of periosteum (Fig 2B). The addition of the strip of periosteum allows for maximal control of the graft during intra-articular tunnel passage while also allowing for a more robust soft tissue–to–bone fixation distally in the tibial tunnel. The addition of the periosteum can add another 10 to 15 mm of length to the graft (Video 1).

Fig 2.

(A) Intraoperative confirmation of length of patellar tendon. (B) Tendon harvest in continuity with strip of periosteum. The patient is positioned supine, with the right side of the figure representing the proximal direction.

Tendon graft preparation can be performed in accordance with surgeon preference. We prefer to control the bone plug with 2 No. 2 Ethibond sutures (Ethicon, Somerville, NJ) placed through 2 off-axis 1.2-mm drill holes in the midsubstance of the bone plug. Soft-tissue control is established with placement of 2 running, locking nonabsorbable braided polyester sutures, No. 2 FiberLoop (Arthrex, Naples, FL) (Fig 3).

Fig 3.

(A) Single-plug graft with attached periosteum. (B) Final preparation before passage.

After intra-articular passage of the graft and femoral fixation (screw fixation at the aperture), the knee is cycled while tension is maintained on the previously placed FiberLoop sutures. Cycling allows for elimination of creep and for inspection of the relative isometry of the graft position. Tibial fixation is established with a soft-tissue screw while the knee is flexed to 30° with maintenance of a reverse Lachman vector on the tibia. The tibial fixation can then be backed up with a host of options; we prefer to use interference fixation of the FiberLoop suture tails distal to the tibia with a polyetheretherketone 4.7-mm SwiveLock (Arthrex). Standard soft-tissue closure is undertaken after satisfactory fixation of the graft.

Discussion

We present a useful and simple technique to combat the problems associated with BTB autograft graft-tunnel mismatch with the use of a single tibial-sided bone plug and distal soft-tissue fixation of the graft. The technique involves straightforward preoperative planning based on patellar tendon length measurement on MRI, and in our practice, it is most frequently used in taller patients (>188 cm). Anecdotally, the senior author has been extremely satisfied with the clinical outcomes associated with the technique and, with careful preoperative planning, uses the single–tibial bone plug method frequently as an autograft choice in primary ACL reconstruction. Any graft-tunnel mismatch issues associated with excessive patellar tendon length, along with all of the donor-site morbidity that surrounds patellar bone plug harvesting, can be simultaneously avoided.

Graft-tunnel mismatch can often be problematic during endoscopic ACL reconstruction, resulting in a bone plug recession or protrusion from the tibial tunnel, leading to inadequate osseous fixation. Graft protrusion will often occur as a result of excessive patellar tendon length or when an inappropriate intraosseous tibial tunnel length is chosen. Previous studies have identified numerous solutions to this surgical dilemma, including tibial tunnel bone grafting⁵ and femoral bone plug recession.⁶ However, recent research has focused on methods aimed at avoiding this problem altogether with appropriate preoperative planning techniques. These studies have focused on exploiting patient factors,⁷ such as height and weight, alone or in combination with preoperative imaging characteristics of the patellar tendon⁸ to properly identify the length of the overall graft construct. Importantly, patient height and MRI measurements of the patellar tendon's length have been shown to adequately predict the overall size of the graft. These more recent reports have demonstrated successful techniques for identifying the potential for graft-tunnel mismatch but have not offered surgical solutions for patients with excessively long patellar tendons. Other solutions, commonly proposed, involve increasing the overall tibial tunnel length with adjustment of the angle at which the tibial tunnel is drilled or twisting the BTB graft on itself after femoral fixation. These techniques may lead to decreased graft obliquity and possible alteration in the biomechanical properties of the bone-tendon interface of the graft.⁹ Our straightforward technique maintains graft obliquity with the use of a more standard tibial tunnel trajectory and further eliminates any of the concerns associated with excessive graft twisting.

We also believe that the added advantage of decreasing the morbidity associated with patellar plug harvest pays dividends in the perioperative period. Specifically, avoiding bony harvest from the patella may decrease the amount of soft-tissue swelling and improve the patient's ability to control the quadriceps muscle. Compliance with early rehabilitation exercises becomes more facile and improves early objective satisfaction. Given this fact, we believe that harvesting a single plug from the tibial side is more advantageous than ACL reconstruction with a quadriceps tendon, which also uses hybrid graft fixation with both bone and soft-tissue interfaces, respectively, on the femoral and tibial side.¹⁰ Furthermore, avoiding bone plug harvest reduces the potential of donor-site morbidity of chronic anterior knee pain and patellar fracture.¹¹ Chronic anterior knee pain can be a significant disability after ACL reconstruction, especially in patients involved in high-level athletics.¹² More importantly, this single-plug technique avoids the disastrous complication of patellar fracture, which has been reported in just under 1% of patellar plug harvest patients up to 3 years after bone plug harvest.¹³ This complication can ultimately significantly affect a patient's rehabilitation and occasionally requires a second operation for surgical fixation.

It must be noted that our technique has several advantages over traditional techniques for dealing with the problem of graft-tunnel mismatch (as mentioned earlier) but it is not without limitations. Principally speaking, the primary limitation of this technique surrounds the lack of bone-to-bone healing for the tibial side of the graft, which is often cited as 1 of the primary advantages of using patellar tendon autograft for ACL reconstruction. Another limitation of this technique may occur with inadequate preoperative and/or intraoperative planning because a patellar tendon length of less than 60 mm may result in an excessively short construct that results in insufficient length for ACL reconstruction.

In conclusion, we believe that the described technique provides a safe and facile method for avoiding graft-tunnel mismatch in patients undergoing ACL reconstruction with autogenous patellar tendon in the setting of excessive patellar tendon length. The technique allows for osseous aperture fixation at the femoral tunnel, as well as maintenance of proper tibial tunnel obliquity, and avoids the complications associated with bone plug harvest from the patella.

Supplementary Data

Video 1

Preoperative patellar tendon length measurement to ensure proper patient selection and ensuing single–bone plug harvest from tibia. The tibial plug is harvested in a standard fashion, followed by excision of the graft with the requisite continuum of periosteum from the anterior portion of the patella. This continuous patch of periosteum offers greater control of the graft. The video concludes with final views of the graft after preparation on the back table.